LONDON – Eight healthy babies have been born in the UK, aided by experimental techniques designed to prevent mothers from transmitting severe rare diseases to their offspring through DNA, researchers have announced.

The majority of DNA resides within the nuclei of our cells and is inherited from both our mothers and fathers—essentially, it shapes who we are. However, mitochondria, the cell’s energy-producing structures, also contain DNA outside the nucleus. Mutations in this mitochondrial DNA can lead to various illnesses in children, resulting in symptoms like muscle weakness, seizures, developmental delays, major organ failure, and even death.

In vitro fertilization (IVF) testing typically helps identify these mutations, although there are instances where this is not evident.

Researchers have pioneered methods to circumvent these issues by employing healthy mitochondria from donor eggs. They reported their findings in 2023 in an article detailing the birth of the first babies born using this technique, which involves extracting genetic material from the mother’s eggs or embryos and transferring it to a donor egg or embryo possessing healthy mitochondria, while discarding the bulk of its original DNA.

Dr. Zev Williams, head of the Fertility Center at Columbia University and not involved in this study, stated that this research “marks a significant milestone.” He believes that broadening reproductive choices will allow more couples to achieve a safe and healthy pregnancy.

This method results in an embryo containing DNA from the mother, the father, and the donor’s mitochondria—an approach that became legally viable in the UK after law changes in 2016. Similar procedures are also permitted in Australia, though they remain banned in many countries, including the US.

Experts from Newcastle University in the UK and Monash University in Australia reported in the New England Journal of Medicine that they successfully implemented these new methods for fertilizing embryos from 22 patients, with one woman still pregnant.

One of the eight babies born exhibited unexpectedly high levels of abnormal mitochondria, according to Robin Lovell-Badge, a stem cell and developmental genetics scientist at the Francis Crick Institute, who was not involved in the research. While these levels are not currently deemed harmful, monitoring is required as the baby grows.

Andy Greenfield, a reproductive medicine expert at Oxford University not associated with the research, emphasized its significance, noting that mitochondrial replacement techniques are primarily used in other settings aimed at avoiding genetic illnesses, like early-stage embryo testing.

“This technique was certified a decade ago, so we have all been anticipating this report,” he shared with NBC News via email. “Fortunately, the children appear to be healthy.”

Long-term follow-up with these children is essential as keeping them healthy is a priority, he emphasized.

Lovell-Badge noted that the donor DNA’s contribution is minimal, asserting that the child will not exhibit characteristics from the women who provided the healthy mitochondria. The donor genetic material constitutes less than 1% of the DNA in babies conceived using this technology.

“In comparison, if you received a bone marrow transplant from a donor, you would possess significantly more DNA from other individuals,” he explained.

In the UK, all couples seeking childbirth via donated mitochondria must obtain approval from the national fertility authority.

Concerns have been raised by critics, who warn that the long-term effects of such innovative techniques on future generations remain uncertain.

“At this time, clinical application in the US is not allowed, mainly due to regulatory restrictions regarding genetic modifications to embryos,” Dr. Williams from Columbia said via email. “Whether this situation will evolve remains unclear and is subject to ongoing scientific, ethical, and policy discussions.”

For almost ten years, Congress has included provisions in the annual funding bill that prevent the FDA from accepting applications related to clinical research protocols involving the intentional creation or modification of human embryos to incorporate genetic alterations.

However, in jurisdictions where such methods are allowed, advocates argue they can offer a promising option for some families.

Liz Curtis, whose daughter Lily passed away from mitochondrial disease in 2006, is collaborating with other families affected by these disorders. She expressed the devastation of receiving a diagnosis indicating that death was inevitable for an infant without intervention.

Curtis reflected on how the diagnosis “turned our world upside down, and yet there was minimal discussion about it, what it entailed, and how it would affect Lily.” Following this experience, she founded the Lily Foundation in her daughter’s honor to raise awareness and support regarding the disease, alongside her latest initiatives at Newcastle University.

“This development is incredibly exciting for families who have little hope for a positive outcome,” Curtis remarked.

The UK fertility authority, which oversees human fertilization and embryology, endorsed the findings, noting that this technique might only be accessible to individuals with a high risk of transmitting disease to their children.

As of this month, 35 patients have been approved to undergo the procedure.